why not use teagan as new babys middle name also.. it is hard isnt it.. i mean my cousin is called grace and my middle name is grace.. x
Maybe having different letter that ends in gan sound might help?

Just so you know, I've tried being creative with names and whenever I have done so,.I've come u with : bambi-candice, angel-starr, and ocean-raine which have all in turn been said they sound like "p*rn star" names hence why I go for more traditional .. I also like river lol

Also I think the problem is you already have 2 daughters and both have unique names, you give your 3rd one a name already used by the eldest and you can cause drama. The middle one may be upset that her name isn't being use, the youngest might be upset that she doesn't have a unique name, and the oldest might be upset that you reused her name.

Every child used to be named after their mother or father. Middles names existed so that each child could actually be identified. So, if the father was named John and had two sons, they would be John Samuel and John Alexander. Anyways, all of this is to say that there is some historical weight to what you want to do. If it means so much to you, go for it. Some people on nameberry have very specific naming rules they live by, doesn't mean they are right though. I can't imagine actually having a negative feeling towards sharing a name with my sister, it actually would probably make me feel more connected to her.

I'm not a fan of having naming rules because I figure, why limit your options? That being said, I would never give my kids names that have the same root. Like, I would (in theory) use Leonor and Leo, but not Leo & Levon.
So, no, I wouldn't re-use a name within my kids' names. I know people who have, and it's fine, and I don't think any of the kids are scarred for life because of it, but with all the name options out there, I couldn't imagine using a name more than once.